Video and other types of media are sensitive to packet loss and any entertainment-caliber video service should provide essentially loss-free video delivery from the media source to the media receiver(s). Packet loss can be due to congestion, link errors, and re-routing events. Individual losses or short burst losses can be adequately repaired with Forward Error Correction (FEC) or selective retransmission techniques, depending on the exact nature of the error and the delay in the network.
Selective retransmission is workable only where there is a very short round-trip time between the receivers and the transmitter. In addition, it is difficult and complex to limit the duration of certain outages in packet networks through techniques like Multi-Protocol Label Switching (MPLS) or IP Fast ReRoute (FRR).
Outages in a packet-switched or label-switched core network are usually due to a link or path failure or device/interface failure. Measurements from real deployments show that it usually takes between 50 and 500 milliseconds (ms) to restore the data path, or converge to a new one, and resume packet transmission. The packets that are sent or in flight during the outage are usually lost. In order to provide a robust video delivery, these losses should be repaired within the time frame that would satisfy the real-time requirements of the video application.